With expansion of home care and community medicine (doctors' offices, clinics, etc.) and growing numbers of early diagnoses and highly urgent clinical laboratory tests, etc., even persons other than clinical laboratory test experts have demanded, in recent years, an analysis apparatus capable of simply and rapidly performing highly precise measurement. Thus, an analysis apparatus intended for POCT (Point of Care Testing) is in the limelight, which is capable of performing highly reliable measurement in a short time without complicated procedures. In general, POCT is a generic name for “near-patient” tests such as tests conducted in practitioners' or specialists' offices, wards, and outpatient clinics. This method attracts attention as being highly useful for improving the quality of clinical practice because the doctor can make an on-the-spot judgment on test results, perform rapid treatment, and even monitor a treatment process or prognosis. The POCT can reduce costs required for transportation of samples or for facilities or costs required for unnecessary tests, compared with tests conducted in the central laboratories of hospitals or the like, and can allegedly cut back on total amounts of test costs. The POCT market has rapidly expanded in the U.S. with progress in the streamlining of hospital management and is expected to grow worldwide, including Japan.
Dry analysis devices typified by chromatographic test strips as immunosensors are capable of analyzing an analyte in a test solution only by simple procedures such as dropwise addition of a sample solution (e.g., blood or urine) to be measured onto the analysis device, without the need of preparing reagents, and are very useful for a convenient and rapid analysis. Therefore, a large number of such devices are now put in practical use as a representative of POCT. Moreover, the market demands more highly precise measurement in a shorter time, in addition to measurement that can be achieved anytime and anywhere by anyone. Also, analysis apparatuses have been proposed, which specialize in optical reading from the analysis devices.
Hereinafter, a conventional method for measuring an immunochromatographic test strip will be described. When a sample solution containing a cellular component is analyzed by a conventional approach, a structure which removes the cellular component in advance or a structure having a cellular component separating member provided in a chromatographic test strip is required. However, such a method disadvantageously requires a time for removing the cellular component in advance or disadvantageously requires the sample solution in non-small amounts in consideration of samples absorbed in the cellular component separating member. Thus, as disclosed in Japanese Patent Nos. 3655283 and 3813150, a method has been proposed, which includes contracting a cellular component and then developing a sample solution.
FIGS. 10(a) and 10(b) are an exploded perspective view and a perspective view, respectively, of a conventional immunochromatographic test strip. FIGS. 11(a) and 11(b) are respectively a cross-sectional view of the immunochromatographic test strip, wherein FIG. 11(a) is a diagram showing an image of red blood cells in a gap portion after blood introduction, and FIG. 11(b) is a diagram showing an image of the mixed state of plasma and a labeling reagent in the gap portion after plasma introduction.
An immunochromatographic test strip (hereinafter, simply referred to as a test strip) 100 using an antigen-antibody reaction includes: a gap portion 8 formed by a transparent space forming member 7 which is provided on one side in the longitudinal direction of the test strip 100, has an air vent 10, and holds a cell shrinkage reagent 9 capable of being eluted due to a sample solution 50; a developing layer 2 which is provided to extend from the central part in the longitudinal direction of the test strip 100 to the other side of the test strip and develops the sample solution 50 through a capillary phenomenon; a developing layer support 1 which is provided in the whole area in the longitudinal direction of the test strip 100; a labeling reagent holding part 3 which contains a substance (e.g., a colloidal gold labeling reagent) specifically binding to an analyte contained in the sample solution 50 flowing to the upstream region of the developing layer 2; a reagent-immobilized part 4 which immobilizes the analyte bound with the labeling reagent; a liquid absorption part 19 which finally absorbs the sample solution 50; a transparent liquid-impermeable sheet 5 which covers the developing layer 2; and so on. Reference numeral 6 in FIGS. 10 and 11 depicts a sample introduction part which introduces a sample solution therethrough, and this sample introduction part is formed by an opening at the end of the gap portion 8. The amount of the labeling reagent immobilized on the reagent-immobilized part 4 can be measured to thereby determine the concentration of the analyte in the sample solution 50.
In this context, as shown in FIGS. 10(b) and 11(a), the test strip 100 is kept in a horizontal posture, while the sample solution is introduced to the sample introduction part 6 and subjected to a reaction or development.
Specifically, when blood as an example of the sample solution 50 is introduced to the sample introduction part 6, the sample solution 50 reacts with the cell shrinkage reagent 9 in the gap portion 8. Then, the sample solution 50 flows through the developing layer 2 and elutes a colloidal gold labeling reagent in the labeling reagent holding part 3. Next, by this elution of the labeling reagent, a colloidal gold-labeled antibody and an analyte (antigen) contained in the sample solution cause a binding reaction during which the reaction solution further flows through the developing layer 2 and arrives at the reagent-immobilized part 4. Then, the complex of the colloidal gold-labeled antibody and the antigen binds to an antibody immobilized in the developing layer 2. Through these processes, a color of the colloidal gold appearing in the reagent-immobilized part 4 can be detected by visual observation or using an optical detector to thereby confirm the presence or concentration of the analyte in the sample solution 50. In the test strip 100, the gap portion 8 formed by the space forming member 7 holds the cell shrinkage reagent 9, which in turn contracts red blood cells as a cellular component in blood into a size smaller than the pores of the developing layer 2. As a result, the whole blood is favorably developed to the developing layer 2.